Gamak Bay Research Articles

Study on the Selection of Fishing Ground by Fishing Vessel Fishery in Gamak Bay, South Sea of Korea

Study on the Selection of Fishing Ground by Fishing Vessel Fishery in Gamak Bay, South Sea of Korea

Effects of hypoxia on copepod egg hatching success: An in situ study

Hypoxia is a global concern, affecting marine ecosystems. In this study, we investigated the effect of low Oxygen concentration on the egg hatching rate of Acartia erythraea in Gamak Bay, where hypoxia frequently occurs in summer. Three in situ experiments were conducted in June and August 2013 and July 2014. Environmental parameters, including the water temperature, salinity, dissolved Oxygen (DO) concentration, and pH, were measured during the experiments. Hypoxic conditions had a significant negative impact on the hatching rate of A. erythraea eggs; hatching rate was positively correlated with the DO concentration (r = 0.843, p < 0.01) and pH (r = 0.600, p < 0.01). These findings suggest that hypoxia has significant negative impacts on recruitment of planktonic A. erythraea, with potential implications for overall plankton and nekton dynamics.

Spatial distribution of phytoplankton in Gamak Bay in spring, with emphasis on small phytoplankton

Spatial distribution of phytoplankton in Gamak Bay in spring, with emphasis on small phytoplankton

Impacts of hypoxia on the mesozooplankton community structure in a semi-enclosed bay

Gamak Bay is frequently affected by hypoxia in summer. Therefore, this study aimed to examine the effect of hypoxia on the mesozooplankton community of this region. Mesozooplankton samples were obtained biweekly (28 times) at a hypoxic station (inner bay) and a normoxic station (middle bay) using a conical net (mesh size 200 μm; mouth diameter 30 cm) from April 2020 to April 2021. In the inner bay, hypoxia was observed a total of five times between early June and late September, whereas no instances of hypoxia were detected in the middle bay. During the hypoxic period, mesozooplankton abundance was higher in the inner bay than the middle bay (p &amp;lt; 0.05). During the normoxic period, there was no difference between the inner bay and the middle bay (p &amp;gt; 0.05). The dominant species in the hypoxic period were three species of cladocerans (Pleopis polyphemoides, Pseudoevadne tergestina, Penilia avirostris) and the copepod Acartia sinjiensis. The abundance of cladocerans was higher in the inner bay, and that of A. sinjiensis was higher in the middle bay (p &amp;lt; 0.05). In addition to water temperature, salinity, and size-fractionated Chl-a concentration, mesozooplankton abundance was also significantly correlated with the bottom DO concentration. Collectively, our findings suggest that hypoxia can affect mesozooplankton abundance and occurrence times.

C, N, and P Mass Balances in the Bottom Seawater–Surface Sediment Interface in the Reducing Environment due to Anoxic Water of Gamak Bay, Korea

Current mass balances of C, N, and P were estimated using a model (Fluxin = Fluxout + ΔFlux) from Gamak Bay, Korea, in August 2017, where eutrophication and reducing conditions are prevalent. To examine the current fluxes of particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP), sinking and re-floating sediment traps were deployed, a sediment oxygen demand (SOD) chamber experiment and ex-situ nutrient incubation experiment were conducted, and Fick’s first law of diffusion was applied. The principal component analysis and cluster analysis were performed to identify the three groups of water masses based on the characteristics of the bay, including the effects of the reducing environment due to the anoxic water mass using 14 bottom water quality parameters. In the reducing environment (sampling point GA4), the SOD20 flux was 3047.2 mg O2/m2/d. Additionally, the net sinking POC flux was 861.0 mg C/m2/d, while 131.8% of the net sinking POC flux (1134.5 mg C/m2/d) was removed toward the overlying water. This indicates that the organic matter that had been deposited was decomposed as a flux of 273.6 mg C/m2/d. The net sinking PON flux was 187.9 mg N/m2/d, whereas 15.8% of the net sinking PON flux was eluted, and 84.2% remained in the surface sediments. The dissolved inorganic nitrogen (DIN) elution flux from the surface sediments consisted of NH4+ elution (33.7 mg N/m2/d) and NOx− elution (−4.1 mg N/m2/d) fluxes. Despite the net sinking POP flux being 26.0 mg P/m2/d, the 47.7 mg P/m2/d of DIP elution flux (179.5% of the net sinking POP flux) was eluted to the overlying water. Similar to C mass balance, the additional elution flux occurred. Therefore, severe eutrophication (16.5 of the Okaichi eutrophication index) with the lowest N:P ratio (2.6) in GA4 was noted. This indicates that not only the freshly exported organic matter to the surface sediments but also the biochemical processes under anoxic conditions played an essential role as a remarkable nutrient source–particularly P–for eutrophication in Gamak Bay, Korea.

Characteristics of Hypoxic Water Mass Occurrence in the Northwestern Gamak Bay, Korea, 2017

Characteristics of Hypoxic Water Mass Occurrence in the Northwestern Gamak Bay, Korea, 2017

Egg production and hatching patterns of Acartia erythraea (Copepoda, Calanoida), with a note on its two egg types, in a eutrophic bay in Korea

Abstract Acartia erythraea, a copepod species commonly found in the summer, was sampled weekly using a conical net, in Gamak Bay (southern Korea) from 19 July to 14 November 2013. Egg production rate (EPR) and hatching success rate (HS) were estimated weekly during the study period, for egg types with distinct surface morphologies, i.e. smooth or spiny. EPR ranged from 1.0 to 25.0 eggs female−1 day−1 with a mean of 12.0 eggs female−1 day−1. The weight-specific growth rate (WSGR) ranged from 0.01 to 0.19 day−1 with a mean value of 0.09 day−1. Of these, all the eggs were smooth until August, whereas spiny eggs were produced from September, and the spiny eggs contributed 88% of the total eggs in November. Both egg types hatched within 12 to 48 h, and the average HS was 80% or higher. The EPR and WSGR were significantly related to water temperature but weakly related to chlorophyll-a concentration. Contrary to previous studies, our findings suggest that it is impossible to determine whether an egg is subitaneous or diapause based on the egg surface structure. Spines on the surface of A. erythraea eggs in Gamak Bay could be an adaptation to seasonal variations and a rapidly changing coastal environment.

Seasonal changes in copepod biomass and production in Gamak Bay, Korea

To better understand the ecological functioning of the coastal ecosystem in Gamak Bay on the southern coast of Korea, seasonal changes in the density, biomass, and secondary production of the copepod community were investigated. Environmental measurements (temperature, salinity, and chlorophyll a) and copepod sampling were performed seasonally from January to December 2006. The mean density of copepods (excluding nauplii) varied from 949 to 5,999 ind · m−3; copepod density was at its highest from March to July. The copepod community comprised 32 taxa, including Calanoida, Cyclopoida, and Harpacticoida. The predominant species were Paracalanus parvus s. l., Acartia omorii, Eurytemora pacifica, Oithona similis, A. erythraea, Centropages abdominalis, Pseudodiaptomus marinus, and Calanus sinicus. There were significant spatial and seasonal variations in copepod total biomass, which ranged from 0.33 to 43.10 mg C m−3. Mean secondary production of the copepods in Gamak Bay, estimated as 2.05 ± 1.63 mg C m−3 d−1 using the Huntley and Lopez growth model, was over 2 times higher than the value given by application of the Hirst and Bunker model (1.09 ± 0.85 mg C m−3 d−1). The daily production rate to biomass (P/B) ratio varied between 0.08 and 0.86 d−1 (Huntley and Lopez model), and 0.18 and 0.33 d−1 (Hirst and Bunker model). Our results emphasize the ecological significance of using models to estimate the secondary production of copepods and provides the first report of copepod production in Gamak Bay.

Short-term variation in abundance of four Acartia species (Copepoda, Calanoida) in a eutrophic bay.

The short-term variation in the abundance of Acartia copepods in the eutrophic Gamak Bay of South Korea was investigated with weekly measurements from October 2007 to September 2008. During this period, four Acartia species (A. erythraea, A. ohtsukai, A. omorii, and A. sinjiensis) were recorded as showing seasonally different peak abundance. The abundance of A. erythraea and A. sinjiensis was high in autumn, whereas that of A. omorii was high from winter to spring. In summer, A. erythraea, A. ohtsukai, and A. sinjiensis coexisted at peak abundance significantly related to water temperature and salinity. Results from the response curves of the four Acartia species to water temperature and salinity suggest that A. erythraea and A. sinjiensis increased in abundance at water temperatures >18 °C, whereas A. ohtsukai increased in abundance at water temperatures >27 °C. The occurrence of A. erythraea, A. ohtsukai, and A. sinjiensis decreased with increasing salinity, but chlorophyll-a concentration showed no effect on occurrence. Despite these findings, the coexistence of the three ecologically similar species may be due to prey abundance in summer and autumn (chlorophyll-a concentration >10 µg L−1). Notably, the wide range of the response curve of A. omorii indicates its occurrence at higher salinity levels than other species.

가막만 연구의 변천과 앞으로의 과제

본 연구에서는 지난 40여년간 발표된 88편의 학술논문과 기타 학위논문, 기술연구보고서 등의 자료를 분석하여 가막만 환경의 과거와 현재의 모습을 진단, 평가하고, 앞으로 가막만의 환경 회복을 위해 필요한 연구과제를 모색하였다. 가막만에서는 해양 및 어장의 환경 또는 수질과 관련한 연구가 가장 많이 이루어졌고, 다음으로 적조, 해양생태계 모델링, 양식생물(주로 굴 등의 패류), 해수유동 등의 순이었으며, 이들 조사연구는 하계에 이루어진 경우가 가장 많았다. 이와같이 가막만 조사가 타 계절에 비해 하계에 많은 것은 적조나 굴의 폐사 등이 주로 하계를 중심으로 발생하고 있다는 사실과 무관하지 않은 것으로 판단되었다. 또한 가막만의 수질은 현재 굴 양식에는 큰 지장이 없는 COD 환경기준을 유지하고 있으나, 수질을 보다 더 개선하기 위해서는 만내로 유입되는 육상기인 오염물질의 부하를 삭감할 필요가 있는 것으로 나타났다. 한편, 가막만에서는 빈산소 수괴의 발생과 어패류의 폐사가 앞으로 해결해야 할 주요 과제인 것으로 밝혀졌다. 따라서 가막만 환경문제의 극복을 위해서는 우선 가막만내로 유입하는 육상 오염원을 철저히 차단하고 빈산소 수괴의 발달을 억제하기 위한 공학적인 접근(예를 들면 작령공(作澪工) 또는 aeration이 필요할 것으로 판단되었다. 뿐만 아니라 가막만의 환경용량에 적정한 양식시설의 배치와 어장관리, 나아가 양식생물에 의한 자가오염의 방지를 위한 어장정화사업도 필요할 것으로 생각되었다. 이러한 관점에서 앞으로 가막만의 환경을 위해 필요한 연구과제는 연구자와 지역사회 구성원들이 함께 지혜를 모아 발굴하여야 하며, 연구는 체계적이고도 지속적으로 이루어져야 할 것으로 판단되었다.

Seasonal variation of the zooplankton community of Gamak Bay, Korea

The seasonal variation in the zooplankton community and hydrographic conditions were examined in three regions (inner, central, and outer regions) of Gamak Bay, Korea. Zooplankton samples were collected over a period of 12 months from January to December 2006. The hydrographical parameters of temperature, salinity, chlorophyll-a concentrations, dissolved oxygen, and chemical oxygen demand were measured. The total zooplankton density varied from 411 to 58,485 ind. m-3, with peaks in early summer. A total of 65 taxa accounted for approximately 86.9% of the annual mean zooplankton density: Noctiluca scintillans (30.9%) Paracalanus parvus s. l. (24.3%), Acartia omorii (11.9 %), Eurytemora pacifica (5.7%), cladocerans (4.1%), cirriped larvae (3.8%), Oithona similis (3.7%), and Pseudevedne tergestina (2.5%). Copepods dominated numerically throughout the year and comprised 54.3% of the total zooplankton. Most of the dominant copepods showed a well-defined seasonal pattern. The density and diversity of zooplankton in Gamak Bay were influenced by the hydrographic environment that was subject to significant spatial and temporal variations. Multivariate statistics showed that seasonal temperature was the most significant predictor of zooplankton taxa, density, and diversity, as well as the density of dominant taxa. Our results suggest that fluctuations in the zooplankton populations, particularly copepods, followed progressive increments in the temperature and COD concentrations.

정기 환경조사 자료를 이용한 전남 양식어장 입지의 적합성 평가

This study was conducted to evaluate the locational suitability of aquaculture grounds in Jeonnam coastal area using seawater and sediment quality monitoring data from 2016 to 2018. It was evaluated that the water temperature of February and August in the inner area of Gamak, Yeoja, Deukryang, and Hampyung bay was not suitable for rockfish based on its tolerable temperature range. It is also revealed that the concentrations of dissolved inorganic nitrogen and phosphorus are lower than the suitable laver growth around the coast of Wando, Jindo, especially in Goheung during the culturing period. Moreover, it was evaluated that the status of sediment eutrophication in the inner area of Yeoja, Deukryang, and especially in Gamak bay could affect the growth of mussel or blood cockle by discharging unfavorable gas if anaerobic condition was formed.

2017년 가막만 북서내만해역 표층 해저퇴적물의 부영양화 현황 및 정화·복원 방향

전남 여수시 가막만은 패류 양식장 등의 수산자원의 보호를 위해 환경보전해역으로 선정되었다. 그러나 가막만 북서내만해역은 매년 부영양화와 관련하여 해양환경에 대한 악영향이 지속되어 온 해역이다. 이에 여수시는 과거 가막만 선소 내측과 북서내만해역에서 해양오염퇴적물의 정화·복원사업을 실시하여, 해양환경이 개선된 것이 보고 된 바 있다. 그러나 근래에는 빈산소수괴, 황화수소 등의 악영향이 되풀이되고 있는 실정이다. 이러한 원인으로는 해당 사업이 유기물의 유입원에 대한 충분한 조사 없이 진행되었기 때문으로 판단된다. 한편, 2013년부터 해양수산부는 정화지수를 적용하여 정화·복원사업의 범위를 산정하도록 규정하고 있다. 이에 본 연구는 가막만 북서내만해역의 해저퇴적물 중 유기물 항목들에 대해 정화복원지수(CIET)를 적용하여 해양오염퇴적물 범위를 산정하고, carbon/nitrogen 비와 과거 문헌조사를 통해 유기물 유입원에 대해 토의하여 향후 개선방안을 논의해보고자 한다. CIET 및 C/N 비 적용결과, 해저퇴적물 중 점오염원/비점오염원의 영향을 받은 선소 내측해역과 식물플랑크톤과 양식장으로부터의 영향을 받은 장도 남측, 호도리 측, 북서내만해역 중앙 측에서 정화·복원이 필요할 것으로 사료된다. 외부오염원 개선을 위해 가막만 인근의 하수관거 개선이 제안되었으며, 내부오염원 개선을 위해 준설 및 해저퇴적물 개선제 사용, 양식 어장의 휴식이 제안되었다.

In situ production of dissolved organic carbon (DOC) by phytoplankton blooms (Cochlodinium polykrikoides) in the southern sea of Korea

We measured dissolved organic carbon (DOC) concentration in the surface seawater of Gamak Bay located in the southern Korea and groundwater nearby the bay in August 2007 to determine effect of harmful algal blooms on DOC distribution in the surface waters. The average of DOC concentration in the bloom stations (157 ± 25 μM) was 1.6-fold higher than that of the non-bloom stations (96 ± 15 μM). The DOC concentrations in groundwater and offshore seawater were significantly lower than those in the bloom stations but showed similar values in the non-bloom stations. The facts that salinity showed no significant relationship with DOC but Chl-a showed a significant correlation with DOC, indicate that the major source of DOC in the bloom stations may be in situ phytoplankton production rather than groundwater and/or river water. In addition, DOC showed a strong relationship with peridinin (biomarker of dinoflagellate) but showed no relationship with fucoxanthin (biomarker of diatom). These results suggest that the DOC distribution in Gamak Bay seems to be controlled by in situ phytoplankton production by dinoflagellate rather than diatom. Therefore, distributions of DOC in the southern sea of Korea during bloom season may be controlled by biological processes such as the intensity and duration of dinoflagellate.

The Relationship between Germination of Dinoflgellate Cysts and Vegetative Cells in Gamak Bay

The Relationship between Germination of Dinoflgellate Cysts and Vegetative Cells in Gamak Bay

가막만 담치 양식활동이 춘계 저산소현상과 저서성 유공충 군집에 미치는 영향

가막만 담치 양식활동이 춘계 저산소현상과 저서성 유공충 군집에 미치는 영향

다변량분석에 의한 여수 백야도 어류양식장의 해양 환경분석

This study was conducted to evaluated the surface(10 variables) and bottom(10 variables) water quality, and sediment(3 variables) in the cage fish farm off Baegyado in Gamak Bay using a multivariate analysis from January 2013 to November 2014. Generally, the environmental data did not show a certain tendency by months during two years investigated. The pairwise simple correlation matrices among variables were also shown. The first four principal components of the surface water in 2013 explain 93% of the total sample variance; the first principal component(z₁) showed the freshwater inflow and/or precipitation, z₂, z₃ and z₄ related to freshwater inflow and/or precipitation, organic matters and eutrophy, respectively; the first four principal components of the bottom water in 2013 explain 93% of the total sample variance; the z₁, z₂ and z₄ related to freshwater inflow and/or precipitation, and z₃ water temperature. In 2014, at the surface water the first three principal components explain 87%; the z₁, z₂ and z₃ related to water temperature, eutrophy and freshwater inflow and/or precipitation, respectively; at the bottom water the first three principal components explain 93%; z₁, z₂ and z₃ related to water temperature, freshwater inflow and/or precipitation and eutrophy. Half of the principal components related to freshwater inflow and/or precipitation.

First Record of Box Jellyfish, Carybdea brevipedalia (Cnidaria: Cubozoa: Carybdeidae) from Korean Coastal Waters: Morphology and Molecular Descriptions

We firstly described a box jellyfish, Carybdea brevipedalia collected from the southern coasts of Korea. It is morphologically characterized by gastric phacellae, a special digestive system of cubozoan jellyfish, and velarium, the thin muscle flap forming the opening of the subumbrellar cavity. The phacellae are linear-shaped, comprising numerous cirri branched from multiple roots. Each root also has multiple numbers of cirrus bundles. Basis of velarial cannels parts into two branches in each octant of velarium. Its geographic distributions were limited to Jejudo and the middle-southern coasts where the organisms are seriously hazardous to bathers in summer. Numerous individuals and/or large-sized populations were observed specifically from beaches at Jeju-do, Namhae-do and a small fishing port of Namildae, while only a small amount of the individuals was observed in Gamak Bay, Jaran- Goseung Bay, and Geoje-do. We confirmed molecular identity of the Korean C. brevipedalia with comparison of nuclear ribosomal DNA sequences. Until now, Carybdea brevipedalia is the only cubozoan species reported to be distributed in Korean waters.

가막만 양식장과 자연 서식지에서의 대형저서다모류 군집구조 차이

본 연구는 가막만에 위치하는 양식장과 자연 서식지(비양식장해역)에서의 저서환경과 저서다모류군집의 차이를 비교하기 위하여 실시하였다. 자연 서식지에서의 조사 정점은 가막만 전 해역에 고르게 분포시켰으며, 양식장 해역은 가막만의 대표적인 양식장인 담치양식장, 굴양식장, 피조개양식장을 대상으로 선정하였다. 자연 서식지 해역과 양식장해역의 퇴적상은 대부분 니질 퇴적상을 보였으며, 평균 유기물함량은 자연 서식지에 비해 양식장해역에서 높게 나타났다. 그리고 양식장해역보다 자연 서식지 해역에서 저서다모류군집의 출현종수와 평균서식밀도가 상대적으로 높게 나타났다. 최우점종은 양식장과 자연 서식지 모두 잠재적 유기물오염지표종인 Lumbrineris longifolia로 나타났으나, 나머지 주요 우점종은 지역간에 약간의 차이를 보였다. 집괴분석 및 nMDS를 이용한 군집구조 분석 결과 지연 서식지 해역은 지역적으로 그룹이 나뉘었으나, 양식장해역의 경우 북서 내만역의 무생물정점을 제외하고 대부분의 정점이 한 그룹으로 묶였다. 또한 상관분석 및 PCA 분석 결과, 자연서식지의 경우 퇴적환경과 저서다모류군집간에 비교적 높은 상관관계를 보였으나, 양식장의 경우에는 낮은 상관관계를 보였다. 즉 가막만 양식장해역에 형성되어 있는 저서다모류군집은 다량의 유기물 유입과 같은 비정상적인 조건 하에 놓여 있음을 의미한다. 따라서 가막만은 생물상이 극히 빈약한 북서 내만역과 함께 양식장해역 역시 지속적인 모니터링을 통한 환경 개선 노력이 필요하다고 생각된다.

A Study on Temporal-Spatial Water Exchange Characteristics in Gamak Bay using a Method for Calculating Residence Time and Flushing Time

A Study on Temporal-Spatial Water Exchange Characteristics in Gamak Bay using a Method for Calculating Residence Time and Flushing Time